Pain perception

The degree of tissue damage is related to the magnitude of the pain stimulus. The site of injury is also important; thoracic and upper abdominal injury is more painful than injury elsewhere. However, the perception of pain is dependent on other factors, e.g. simultaneous sensory input, personality, cultural background and previous experiences of pain.

Management of pain Systemic analgesia

• Opioid analgesics form the mainstay of analgesic drug treatment in intensive care.

• Small, frequent IV doses or a continuous infusion provide the most stable blood levels. Since the degree of analgesia is dependent on blood levels it is important that they are maintained.

• Higher doses are required to treat rather than prevent pain.

• The dose of drug required for a particular individual depends on their perception of pain and whether tolerance has built up to previous analgesic use.

• The use of non-opioid drugs may avoid the need for or reduce the dose required of opioid drugs. This includes paracetamol and non-steroidals, ketamine and a2-agonists such as clonidine and dexmedetomidine.

• Epidural analgesia may be achieved with local anaesthetic agents or opioids.

• Opioids avoid the vasodilatation and hypotension associated with local anaesthetic agents but do not produce as profound analgesia.

• The combination of opioid and local anaesthetic is synergistic.

• Intravenous opioids should be avoided or close monitoring should continue for 24h after cessation of epidural opioids due to the potential for late respiratory failure. Sample regimens are shown opposite.